Method and apparatus for developing electrostatic images



June 21, 1966 K. JONs ETAL 3,257,224

METHOD AND APPARATUS FOR DEVELOPING ELECTROSTATIC IMAGES Filed Dec. 26,1962 5 Sheets-Sheet 1 FIG. I

FIG. 2

INVENTORS KURT .16 s ARTHUR w LFINGER k z- M ATTOR EY METHOD ANDAPPARATUS FOR DEVELOPING ELECTROSTATIC IMAGES Filed Dec. 26, 1962 5Sheets-Sheet 2 FIG?) INVENTORS KURT J5N. ARTHUR WOLFINGER BY J ORNEYJune 21, 1966 oNs ETAL 3,257,224

METHOD AND APPARATUS FOR DEVELOPING ELECTROSTATIC IMAGES Filed Dec. 26,1962 5 Sheets-Sheet 5 INVENTORS KURT J6N, ARTHUR w LFlNGER BY aw... Z.

TTORNEY United States Patent '0 9 Claims. Ci. 117 17.5)

The developers normally used in electrophotography consist of a mixtureof finely divided resinous toner and a carrier for the toner of somewhatlarger particle size than the toner. The carrier is often ofmagnetizable material, e.g. iron filings, in order to enable thedeveloper to be applied with the aid of a rotating magnetic roller tothe surface of a latent electrostatic image.

The magnetic roller, which may be a permanent magnet or may bemagnetized by an electric current, dip into developer powder containedin a trough beneath the roller. The iron filings, carrying the toner ontheir surfaces, adhere in brush-like formation to the magnetic poles ofthe roller and are applied in this form by the rotation of the roller tothe surface of a charged electrophotographic material which has beenexposed imagewise and is traversed over the roller. The toner isattracted electrostatically from the magnet to the photoconductivecoating of the electrophotographic material and a visible image isformed. The developer, depleted in toner, is returned to the trough asthe magnetic roller rotates.

This procedure has the disadvantage that the iron filings adhering tothe roller become progressively depleted in toner and, as a result, thequality of the developed image progressively deteriorates.

It has accordingly been proposed to release the iron filings from anelectromagnetically excited roller by periodically switching off theexciting current so that the roller can be charged anew with fresh tonerfrom the trough in which the developer is agitated to keep it inconstant movement. As such complete interruption of the exciting currentproduces an uneven developing effect, it has also been proposed toswitch off the exciting current at the magnetic poles only which are onthe circumference of Q the semicircle between the point of contact ofthe developer with the electrophotographic' material and the point atwhich the roller dips into the developer in the trough. This proposalalso fails to give the desired results because a certain residualmagnetism persists at the magnetic poles after the exciting current hasbeen switched off, so that the developer powder cannot drop otfcompletely and therefore renewal of the developer takes place to alimited extent only.

Moreover, the iron filings always come to rest at the same place, namelynear the point at which renewed magnetization of the poles occurs sothat the mixing operation in the trough, which can be carried out at alimited speed only and which is intended to load the iron filings withnew toner, cannot take place sufiiciently rapidly. The roller thereforecontinually picks up the toner-depleted iron filings which have justbeen dropped as a result of the demagnetization.

The present invention provides an apparatus for developing latentelectrostatic images comprising a trough to contain a developer mixtureof iron filings and toner powder, an agitator in the trough, anelectromagnetically excited iron roller for picking up developer fromthe trough and transferring it to the electrophotographic material to bedeveloped, the iron roller being made of up of rotor plates having anumber of windings to which exciting current is supplied intermittently,being cut off once in every revolution of the roller and a covering ofsynthetic plastic 3,257,224 Patented June 21, 1956 material, and adeflector plate which coacts with the portion of the roller travelingaway from the electrophotographic material and towards the developercontained in the trough to deflect towards the wall of the troughdeveloper shed by the roller while the current is cut off.

By means of this apparatus, the above-mentioned disadvantages areeliminated. The residual magnetism on the magnetic poles during theperiod in which the current is switched off can no longer hold the ironfilings of the developer because of the plastic coating. The developerpowder shed by the roller is deflected by the deflector plate to a placeremote from the pick-up point of the electromagnetic roller, so that itcan be fully recharged with toner powder by the agitator in the troughbefore it is again taken up by the electromagnetic roller. Rotor platesare understood as components such as are used in the electrical industryfor the production of rotors in electric motors.

The laminations of the roller consists of relatively thin soft ironsheets placed side by side with layers 'of insulating material betweenthem. The shape of these plates corresponds to the cross section of theintended roller. If the notches provided for the windings are even innumber, particularly good results can be obtained. When the individualrotor blades are placed together along the rotational axis and the polesare wound, the magnetic roller to be used as provided by the inventionis formed. Any desired length may be produced.

The covering on the roller mayconsist of any suitable insulating plasticwhich is solid at normal temperatures. Examples of suitable plastics arethermoplastics, such as polyolefins, e.g. polyethylene andpolypropylene, polyvinyl compounds such as polyvinyl chloride,polyamides and polyesters. Good results are also obtained withthermosetting resins, e.g. phenolformaldehyde resins. Particularlyfavorable results are obtained with plastics such as those used forinsulating purposes in transformers; they are described, for example, inthe handbook of Messrs. lSchgamm, Lackund, Farbenfabrik AG,Elektro-Isolierac e.

The plastic coating can be applied by placing the magnetic roller in amold, the gap between the inner Walls of mold and the surface of themagnetic roller being greater than the thickness of the plastic coatingwhich is to be produced on the surface of the roller. The intermediatespaces are now filled with a substance which contains unhardenedcomponents of a resin mixture together with a hardener. The whole isthen allowed to 'stand for 20-30 hours, during which time the plastichardens completely. After removing the roller from the mold, it isadvantageous for'the surface of the plastic coating to be evened andsmoothed by turning. i

The plastic covering may also be applied to the roller by painting on amixture of the plastic substance and a hardener. In such cases, thethickness of the painted coating is advantageously considerably greaterthan the thickness finally required. After hardening out, the surface ofthe plastic coating is again finished by turning and polishing. Plasticcoatings, particularly thermoplastic coatings, can also be applied tothe roller surface in the form of ready made foils by wrapping and,where necessary, fusing. v

The thickness of the plastic coating on the surface of theelectromagnetic roller is generally between 0.2 and 1.0 mm. preferably0.4-0.5 mm., but lesser or greater thicknesses can also be successfullyused.

The surface of the plastic coating on the magnetic roller may be madeelectrically conducting and may be provided with a bias voltage withrespect to the surface of the photoconductive layer of theelectrophotographic material or it may be grounded. This is particularlyadvantageous in the case of the development of latent electrostaticimages which, because of inadequate exposure, have a residual charge inthe image-free parts.

The surface can, for example, be made conductive by treatment with adispersion of silver particles in a suitable dispersion agent, e.g. theso-called Leitsilber (conducting silver), or it can be .coated withmetal. Good results are also obtained by the application of a thin metalfoil to the roller.

The deflector plate extends over the whole width of the electromagneticroller. The distance of the deflector plate from the surface of theroller should be kept as small as possible. The length of the surface ofthe deflector plate over which the toner-depleted carrierruns should beas great as possible. The deflector plate should discharge the carriernear to the wall of the trough. The deflector plate can be joinedunderneath with the normally used securing devices to the wall of thevessel.

The apparatus may include a container for toner powder adjacent thetrough and means for periodically delivering measured quantities oftoner powder from the container to the trough.

One embodiment of developing apparatus according to the invention willnow be described in more detail, by way of example, with reference tothe accompanying diagrammatic drawings, in which:

FIGURE 1 is a transverse section through the developing apparatus,

FIGURE 2 is a plan view,

FIGURE 3 is a longitudinal section through the developing apparatus,

FIGURE 4 shows the current supply member in crosssection, and

FIGURE 4a shows the current supply member in plan view.

As shown in FIGURES 1 and 2, the apparatus includes anelectromagnetically excited roller 1 having a shaft 2 which is journaledin bearings 3 and 4 and is driven by the gears 5, 6 and 7. The windings9 of the roller 1 receive current from a source, not shown, of directcurrent via individual slip rings 10. 1

As shown in FIGURES 3, 4 and 4a, the roller 1 has twelve grooves 9'containing six separate windings which are excited by means of six sliprings 10 which coact with the brushes 26. The roller 1 also has acoating 11 of synthetic plastic material. Between points 12 and 13, theslip rings 10 are provided with means for interrupting the current. Theroller rotates anticlockwise as viewed in FIGURE 4 and, as soon as thewindings 9 have passed the point 13, they are deprived of current. Thedeveloper carried by the roller is then dropped off and is deflected bya deflector plate 14 to the outer edge of the developer trough. Thediscarded developer works its way very slowly back from the outer edgeof the developer trough 14' to the agitator 15 in the trough and istaken up by the agitator and, after intensive mixing, passed to thepoint 12, at which magnetization of the roller recommences, and is theretaken up by the roller. The plastic coating 11 on the magnetic roller 1ensures that after the current has been switched off at the point 13 thedeveloper will not remain attracted by residual magnetism.

The trough is replenished with toner in a simple manner and without dustby the following mechanism:

A container 17 (FIG. 3) contains a certain quantityof toner for purposesof replenishment. As the toner is consumed, the trough is replenishedwith toner from the container 17 by dosing plungers 18. End plates 19 onthe plungers 18 normally close the feed opening 20 in the wall of thecontainer 17 and the plungers carry sealing sleeves 21. The plungers,which are fitted with return springs 24, are actuated by rocker arms 22from a motordriven eccentric 23, which is driven at a speed appropriateto requirements. The toner in the container 17 is agitated by a vane 25which is vibrated by a rocker magnet.

It will be obvious to those skilled in the art that many modificationsmay be made within the scope of the present invention without departingfrom the spirit thereof, and the invention includes all suchmodifications.

What is claimed is:

1. Apparatus for developing latent electrostatic images comprising atrough adapted to contain a developer having a magnetic component, arotatable electrically magnetizable roller mounted in the trough, theroller having a plurality of separate windings and an insulating layeron the roller surface, means for supplying and interrupting an electriccurrent to at least one of the windings during rotation of the roller tothereby successively magnetize and demagnetize portions of the rollersurface, and defleeting means mounted adjacent the roller.

2. Apparatus according to claim 1 in which the insulating layer is aplastic material.

3. Apparatus according to claim 1 including a container adapted tocontain toner mounted adjacent the trough and means for deliveringmeasured quantities of toner to the trough.

4. Apparatus according to claim 1 in which the roller comprises aplurality of rotor plates.

5. Apparatus according to claim 1 in which the roller 15 iron.

' 6. Apparatus according to claim 1 in which the deflecting means is aplate.

7. Apparatus according to claim 1 in which the trough also containsmeans for agitating the developer.

8. A process for applying a developer to a latent electrostatic imagewhich comprises electrically generating a magnetic field in portions ofa surface of a rotatable applicator submerged in a body of developerhaving a magnetic component, rotating the said portions of the surfacecarrying developer thereon into contact with the latent electrostaticimage, rotating the said portions of the surface out of contact with theelectrostatic image and interrupting the electric current, therebyeliminating the magnetic field from said portions of said surface, andpassing excess developer from said portions of said surface back intothe body of developer at a point remote from the initial position of thedeveloper in the body.

9. A process according to claim 8 in which toner is intermittently addedto the body of developer.

References Cited by the Examiner UNITED STATES PATENTS 404,465 6/1889Bradley 310-46 X 500,400 6/1893 Lange.

673,980 5/1901 Engelhardt 310-46 1,048,223 12/1912 Stein 209-2231,177,981 4/1916 Wright 209-219 X 1,362,072 12/ 1920 Arnold 209-2191,371,301 3/1921 Converse 209-219 1,449,371 3/1923 Apple 310-45 X2,449,021 9/1948 Stahl.

2,711,249 6/1955 Laurila 209-219 2,779,306 1/1957 Dunn 11717.5 X2,832,311 4/1958 Byrne 118-637 2,844,489 7/1958 Gemmer 117-22 2,896,1017/1959 Laskin 310-171 2,904,000 9/1959 Fisher et al 118-637 2,956,48710/1960 Giaimo 117-17.5 X 2,975,758 3/1961 Bird 118-637 2,992,733 7/1961Buns et al 209-219 3,003,462 10/1961 Streich 118-637 3,028,266 4/1962Larsh 117-232 3,028,708 4/1962 Vaughan et al 209-219 3,040,704 6/1962Bliss 118-637 3,081,737 3/1963 Frantz et al 1l717.5 X 3,088,386 5/1963Sugarman 118-637 X 3,098,765 7/1963 Keller et al 117-17.5 X 3,152,92410/1964 Wanielista et al. 117-17.5 X

WILLIAM D. MARTIN, Primary Examiner.

G. L. HUBBARD, Assistant Examiner.

8. A PROCESS FOR APPLYING A DEVELOPER TO A LATENT ELECTROSTATIC IMAGEWHICH COMPRISES ELECTRICALLY GENERATING A MAGNETIC FIELD IN PORTIONS OFA SURFACE OF A ROTATABLE APPLICATOR SUBMERGED IN A BODY OF DEVELOPERHAVING A MAGNETIC COMPONENT, ROTATING THE SAID PORTIONS OF THE SURFACECARRYING DEVELOPER THEREON INTO CONTACT WITH THE LATENT ELECTROSTATICIMAGE, ROTATING THE SAID PORTIONS OF THE SUR-